1. Field of the Invention
The invention relates to a solid state imaging device having a reading gate mechanism which can realize miniaturization of it and to a method of driving the device.
2. Related Art of the Invention
Conventionally there are a isolating region for isolating the photoelectric converting parts of pixels and a reading region for reading electric charge stored in the each photoelectric converting parts. These regions are invalid region about sensitivity and saturation characteristics and the area of the photoelectric converting parts is large enough, there is little effect on account of the invalid region and it is not significant for the practical use.
However the miniaturization of CCD is required recently and the above invalid region can not be disregarded and then deterioration of sensitivity and saturation characteristics become large.
That is miniaturization of a solid state imaging device produces insufficient sensitivity due to reduction of the light receiving area, and reduction of the incident light range due to reduction of the pixel area. At present, a CCD solid state imaging device of the 1/3-inch class has the incident light range of about 8 bits. When objects of about 5,000 Lx and 5 Lx exist in the same screen, for example, one of the objects must be sacrificed. This produces a problem peculiar to a photographic process in so-called backlight or excessive forwardlight in the following manner: If the aperture of the lens or the electronic shutter is set to 5,000 Lx, the sensitivity is insufficient for the object of 5 Lx so that an image of the object cannot be taken. By contrast, if the aperture of the lens or the electronic shutter is set to 5 Lx, the object of 5,000 Lx causes a signal charge of an amount exceeding the signal charge amount range of the solid state imaging device to be generated, thereby causing overexposure.
Meanwhile for expanding the incident light range, such method that in one field period two kinds of image signals which have different exposure period to each other are read out to outside is known.
However the prior structure has problem due to miniaturization of an element:
That is in order to improve the sensitivity and saturation characteristics it is suggested to make the photoelectric part large but there are isolation part and reading part separately to each other and the enlarging of the photoelectric part is restricted.